Wells of the type commonly used for fossil fuel exploration and extraction and the like are often several kilometers deep. Typically, these wells or “boreholes” are drilled using pipes (often referred to as “drill strings”) assembled from sections (often referred to as “pipe stands”) connected end-to-end by suitable connection joints. Pipe stands may be about 30 to 45 feet long. To form a borehole, the drill string is rotated such that a drill bit attached to its “downhole” (or operative) end bites into the earth. Additional pipe stands are typically added to the “uphole” (or surface) end of the drill string as the borehole deepens.
Fluid, often referred to as “drilling mud” is typically pumped through an axial bore in the drill string from the surface to the downhole end of the drill string. The drilling mud typically exits the drill string at the downhole end and returns to the surface through the space between the drill string and the borehole. The drilling mud may cool and lubricate the drill bit, power the drill bit (e.g. through hydrodynamic pressure), provide a deposit on the borehole wall to seal the formation, and remove debris from the borehole.
There is a general desire to communicate information from a downhole location of the drill string (e.g. at or near the drill bit) to an uphole location (e.g. a surface location at or near the opening of the borehole). Such communication may permit monitoring of one or more sensors at the downhole location and may also permit control of the drilling operation (e.g. steering, drilling fluid pump parameters, rotational speed and/or the like) based on feedback received from such sensors. Such sensors (which are referred to as measurement while drilling (MWD) sensors) may sense characteristics of pipe string, the drill bit and/or the borehole. Examples of MWD sensor information may include temperature information, pressure information, incline orientation information, azimuthal orientation information, vibration information, drilling torque information and/or the like. In addition to sensor information, it may be desirable to communicate management information from the downhole location to the uphole location. By way of example, such management information may include information related to the sensor information (e.g. the amount of sensor data, the type of sensor data, the transmission order of sensor data and/or the like).
One technique which has been proposed for communicating MWD information from a downhole location to an uphole location involves acoustic telemetry through the drill string. The efficacy of acoustic telemetry depends on the channel through which the acoustic signal travels. In the case of acoustic telemetry through a drill string, the channel or transmission medium comprises the drill string itself, which may exhibit a variety of acoustic properties. In particular, because of the (typically) repetitive spacing of pipe stands and joints therebetween, there are spectral stop-bands (i.e. frequency bands of substantial attenuation) within the frequency spectrum associated with acoustic communication. Between these stop-bands, there are pass-bands which permit the transmission of acoustic energy.
In some circumstances, there is no mechanism for communication down the borehole—i.e. there is no mechanism to communicate information from the uphole location to the downhole location. Without the ability to communicate from the uphole location to the downhole location, it can be difficult to dynamically adapt transmission of MWD information or other information from the downhole location to the uphole location on the basis of information known only at the uphole location.
There is a general desire to communicate information from a downhole location of a drill string (e.g. at or near the drill bit) to an uphole location (e.g. a surface location at or near the opening of the borehole).
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.